A photochromic material has a function of reversibly changing the color or the transparency by being irradiated with light and is used as a light modulation material such as an eyeglass lens or window glass whose color changes depending on the brightness or a sensor material such as an ultraviolet checker or an X-ray sensor. In addition, the applied research to recording media such as optical memories and electronic paper has progressed.
The photochromism is largely classified into positive photochromism and negative photochromism. The former indicates a phenomenon in which a single colorless chemical species is reversely colored with recombination of chemical bonds by irradiation with light. The latter indicates a phenomenon in which a single colored chemical species reversibly changes into colorless by irradiation with light, and development for a reverse photochromic material has been in progress.
Known examples of representative photochromic compounds exhibiting photochromism include a diarylethene-based compound, a spiropyran-based compound, an azobenzene-based compound, a bisimidazole-based compound, and a fulgide compound.
Several examples such as indoline-based spiropyran derivatives (Patent Literature 1) and biimidazole derivatives (Patent Literature 2) have been reported as compounds exhibiting reverse photochromism.
Meanwhile, compounds (Non-Patent Literature 1) useful for fluorescence imaging have been reported as compounds having a merocyanine structure.